The invention concerns an image-inverting system for a sighting telescope, where the image-inverting system has at least two mutually displaceable lenses positioned in at least one tube of the image-inverting system parallel to an optical axis of the image-inverting system, where displacing the at least two displaceable lenses can change the reproduction scale at which an image projected on a first image plane of the image-inverting system is reproduced on a second image plane of the image-inverting system, where the at least two displaceable lenses are arranged in any positions between the first and the second image plane.
The invention further concerns a sighting telescope with an objective and an ocular and a central tube positioned between the objective and the ocular, with an image-inverting system placed inside the central tube, where the first image plane of the image-inverting system faces the objective and the second image plane of the image-inverting system faces the ocular, where an intermediate image projected by the objective on the first image plane is reproduced by the image-inverting system upright on the second image plane.
In the present context, reproduction scale means the ratio of the size of an image of an object on the second image plane of the image-inverting system divided by the size of the image of the object on the first image plane of the image-inverting system.
As an introduction, let it be noted that in this document the term lenses is intended to encompass both single lenses and lenses composed of multiple single lenses (cemented lenses). Such composite lenses can be created by, for example, gluing or cementing two or more single lenses together.
An image-inverting system and a sighting telescope of the type described at the outset are known from EP 1 746 451 B1. In the known image-inverting system, the magnification of the image-inverting system, i.e. the reproduction scale at which an image projected on the first image plane of the image-inverting system is reproduced on the second image plane is changed by displacing the lenses. Increasing the displacement of the lenses increased the zoom range of the known image-inverting system (i.e. the ratio of the maximum reproduction scale quantity-wise to the minimum reproduction scale quantity-wise). However, the increase in displacement entails a lengthening of the image-inverting system and therefore of the image-inverting system tube.
Because of this structural change, realisation of an image-inverting system with a large zoom and a large displacement range of the lenses can lead, especially at the higher magnification settings, to enlargement of the exposed part of the inside of the image-inverting system tube, where disruptive reflections of ambient light not parallel to the optical axis and incident on the image-inverting system can appear. The reflections have a particularly disruptive effect if the displaceable lenses of the image-inverting system are in a position corresponding to the largest magnification of the image-inverting system.
It is therefore an aim of the invention to create a solution that allows good suppression of disruptive light reflections, especially at higher values of the magnification settings, while maintaining a large range for modification of the reproduction scale of an image-inverting system.